1. Field of Invention
The present invention generally relates to copper base alloys having utility in electrical applications and to a process for making the copper base alloys.
2. Description of Prior Art
Electronic components, including connectors, form the basis of information technology, especially in computers. One of the most important considerations in any connector design is to optimize performance at the lowest cost. As computer prices continue to decline, there is a need in the computer industry for, inter alia, alternative materials to those presently used as electrical components that possess the desirable properties of high electrical and thermal conductivity, high yield and tensile strengths, and that are cost effective.
Copper alloys are typically used as connectors and in other electrical and thermal applications because of their generally superior corrosion resistance, high electrical and thermal conductivity, and good bearing and wear qualities. Copper alloys also are useful for their good cold or hot-working properties and machinability.
Copper is alloyed with other metals primarily to increase tensile strength of the alloy. However, electrical and thermal conductivities, corrosion resistance, formability and color of the alloy are strongly affected by alloying copper with other elements. For example, when alloying elements are present in significant concentrations or when low concentrations of deoxidized elements are present, they tend to decrease electrical and thermal conductivity of a copper alloy.
The addition of beryllium to copper results in a significant age hardening response, making these copper alloys one of the few non-ferrous materials that can reach 200 ksi tensile strength. Beryllium copper alloys, however, are very expensive, are limited in their forming ability, and often require extra heat treatment after preparation, further adding to the cost.
Phosphor bronze copper alloys have high strengths, excellent forming properties, and are widely used in the electronic and telecommunications industries. However, the addition of high amounts of tin increases the cost of these alloys.
Copper alloys that include small quantities of tin and zinc provide many desirable properties. One tin brass alloy, commercially available as C42500 (as specified in the ASM Handbook), has a composition of 87%-90% copper, 1.5%-3.0% of tin, a maximum of 0.05% of iron, and a maximum of 0.35% phosphorous, the balance being zinc. The ASM Handbook specifies that the copper alloy designated as C42500 has a nominal electrical conductivity of 28% International Annealed Copper Standard (IACS). This is the traditional way of comparing the conductivity of other metals and copper alloys with high conductivity copper where "pure" copper is assigned a conductivity value of 100% ICAS at 20 degrees Celsius. C42500 also has a yield strength, dependent on temper, of between 45 ksi and 92 ksi. This alloy is used for many electrical applications, such as electrical switch springs, terminals, connectors, and fuse clips. However, its yield strength is lower than desired (i.e., approximately 22 ksi at 40% reduction) for electrical applications.
U.S. Pat. No. 5,853,505 to Brauer et al ("the Brauer '505 patent") describes a tin brass alloy that has been annealed twice at a temperature between about 400 degrees Celsius and 600 degrees Celsius to a grain size of 0.002 mm and contains from 1% to 4% by weight of tin, from 0.8% to 4.0% by weight of iron, up to 0.4% by weight of phosphorous, and the balance being copper.
According to the Brauer '505 patent, when a tin content less than 1.5% is used, the copper alloy lacks adequate strength and resistance to stress relaxation for spring application. The Brauer '505 patent also specifies that the addition of zinc to the alloy would be expected to provide a moderate increase in strength with some decrease in electrical conductivity.
Example 2 in the Bauer '505 patent describes a copper alloy containing 10.4% by weight of zinc, 1.8% by weight of iron, 0.04% by weight of phosphorous, between 1.8% and 4.0% by weight of tin, the balance being copper. An embodiment of the tin brass alloy containing the composition of example 2 in the Brauer '505 patent is commercially available from Olin Corporation as C663. The C663 alloy is available from Olin Corporation with compositions containing from 1.4% to 2.4% by weight of iron, from 1.5% to 3.0% by weight of tin, from 84.5% to 87.5% by weight of copper, up to 0.35% by weight of phosphorous, and the balance being zinc.
Olin Corporation specifies that C663 possesses, depending on the temper, a yield strength of 100 ksi and a tensile strength between 95 ksi and 110 ksi for spring temper, a yield strength of 104 ksi and a tensile strength between 100 ksi and 114 ksi for extra spring temper, and a yield strength of 105 ksi (min) and a tensile strength of 105 ksi (min) for super spring temper. Olin Corporation also specifies that these alloys have an electrical conductivity of 25% ICAS, as annealed. However, these alloys are undesirable because of their high copper content resulting in a higher cost.
There exists a need for a cost effective alternative to existing copper alloys that will still possess high electrical conductivity, high tensile strength, and high yield strength.